1. Field of the Invention
The present invention relates to a bush- and bracket-integrated stabilizer bar in which a stabilizer bar, a portion of a suspension device for a vehicle such as an automobile, is integrated with a rubber bush and a bracket for mounting the stabilizer bar to the vehicle.
2. Description of the Related Art
A stabilizer bar is a member which mainly controls rolling, i.e., rolling movement around the longitudinal axis of a vehicle body. A rubber bush is attached between the stabilizer bar and the vehicle body, and it reduces the propagation of vibration entering the stabilizer bar depending on the conditions of road surface to the vehicle body, and at the same time it flexibly follows-up the movement of the stabilizer bar and supports the vehicle body.
Force is exerted on the rubber bush attached to the stabilizer bar in the direction of rolling of the stabilizer bar depending on the vertical movement of the wheels or the vehicle body. Concurrently, force is exerted on the rubber bush in the vertical direction due to supporting the vehicle body and due to vibration.
The mainstream of a conventional stabilizer bar with a rubber bush has been of a non-bonded type where the stabilizer bar and the rubber bush, and the rubber bush and the bracket are not bonded to each other. Consequently, when water intrudes into the non-bonded portion or when ambient temperature is extremely low, for example, at −30° C., the problem of generating a strange sound due to stick-slip arises.
FIG. 6 shows generated torque (output) with respect to displacement of the stabilizer bar (input such as a kink in the stabilizer bar) when stick-slip occurs to a stabilizer bar with a rubber bush of a non-bonded type. As shown in FIG. 6, a phase shift develops between the displacement of the stabilizer bar and the torque, so that handling performance is affected and steering stability is impaired.
Further, since the stabilizer bar and the rubber bush, and the rubber bush and the bracket are not integrated by bonding, clearances develop between them when a large force is applied to the stabilizer bar. When hard foreign substances intruded into such clearances, there were cases where the stabilizer bar and the bracket were marred and a strange sound generated. Moreover, when hard foreign substances such as sand and stone were left in the clearances, there were cases where malfunctions such as abrasion and breaking occurred.
In order to cope with such problems, various measures by bonding have been conventionally taken. However, they have problems of producing insufficient effects, carrying high costs and others.
(1) Vulcanization Bonding Method (Examined Patent Publication No. 3716750 and Unexamined Patent Publication No. 2006-123818)
Examined Patent Publication No. 3716750 discloses a technology of placing a stabilizer bar and brackets in a mold and performing bonding concurrently with vulcanization molding of rubber bushes. However, since the stabilizer bar and the brackets made of metals are placed in the mold, strength and precision are required for the mold, besides durability of the mold degrades. Moreover, the stabilizer bar usually has a length of about one meter, and thus equipment including the mold and others is made larger and raise the problem of carrying a large cost. Further, paint is usually applied to the stabilizer bar and others after vulcanization bonding is performed, and thus coating defects are likely to develop, for example, between the rubber bush and the stabilizer bar, and incur loss of reliability. In addition, powder painting or cationic painting usually used in painting the stabilizer bar requires a drying or curing process involving high temperature and a long time period, and thus the problem of causing the possibility of heat deterioration of the vulcanization bonded rubber bush arises.
On the other hand, in Unexamined Patent Publication No. 2006-123818, the problems of the upsizing of equipment and others are avoided by performing vulcanization bonding on the brackets when vulcanization molding of the rubber bushes are performed, followed by bonding the rubber bushes with brackets vulcanization bonded thereto to the coated stabilizer bar using a chlorinated rubber based adhesive. However, the present inventors performed a trial manufacture based on the disclosed information and confirmed that heat treatment was necessary to bond the rubber bushes and the stabilizer bar using a chlorinated rubber based adhesive, and that the strength of the rubber bushes degraded by 40 to 50% by heat deterioration. Further, this method requires two sets of a bracket with a rubber bush on the upper and lower sides of a stabilizer bar, and thus it is hard to say that is advantageous from a cost standpoint.
(2) Post Bonding Method 1 (Unexamined Patent Publication No. 2005-319850)
Unexamined Patent Publication No. 2005-319850 discloses a method of performing vulcanization molding on vulcanized rubber as a measure for suppressing the cost rise by the method described in (1). By using the vulcanized rubber, this method resolves the drawbacks such as increased cost through the upsizing of equipment described in (1). However, the present inventors performed a trial manufacture under the same conditions (heating under 10% compression, at 160° C., and for 60 minutes) based on details disclosed therein, and confirmed a significant degradation in strength of rubber bush due to heat deterioration and a problem was raised as to the long-term reliability of the rubber bush. Further, in Unexamined Patent Publication No. 2005-319850, the bush and the bracket are not bonded or fixed together, and thus the problem of generating a strange sound in this portion or the problem of abrasion and breaking caused by intrusion of foreign substances cannot be resolved.
(3) Post Bonding Method 2 (Unexamined Patent Publication No. 2001-270315, Unexamined Patent Publication No. 2006-008082, and Unexamined Patent Publication No. 2006-027311)
Unexamined Patent Publication No. 2001-270315 discloses a method of using a thermosetting adhesive. This method involves curing the adhesive by applying high temperature painting treatment (at 130 to 200° C. for 20 minutes) in a painting step. However, this method also cannot prevent the heat deterioration caused by exposing the vulcanized rubber bush to a high temperature for a long time period. Further, this method also bonds the stabilizer bar and the bush alone and does not bond the bush and the bracket, and thus cannot prevent the strange sound from generating or abrasion and breaking caused by intrusion of foreign substances into this portion. Moreover, painting is performed after the rubber bush is bonded to the uncoated stabilizer bar, and thus painting defects such as leaving portions uncoated are likely to develop at the boundaries of the stabilizer bar and the rubber bush, and corrosion may develop from the painting defect portions, which may raise the problem of, for example, the stabilizer bar getting broken after use for a long time period.
On the other hand, Unexamined Patent Publication No. 2006-008082 and Unexamined Patent Publication No. 2006-027311 disclose methods for bonding a rubber bush by painting a thermosetting adhesive on a stabilizer bar which has been subjected to electrostatic painting or powder painting. However, as a result of performing a trial manufacture based on the details described in these documents, it is found that rubber breaking will not occur, since the adhesion force between the adhesive and the stabilizer bar or between the adhesive and the rubber bush is poor in these methods. Further, in these methods, the bush and the bracket are merely fixed by compression and are not bonded with each other, thus the problem of generating a strange sound in this portion or the problem of abrasion and breaking caused by intrusion of foreign substances still remains unresolved.
(4) Post Bonding Method 3 (Unexamined Patent Publication No. H11-108096)
Unexamined Patent Publication No. H11-108096 discloses a method for bonding chlorination treated rubber bush to a coated stabilizer bar with a thermosetting adhesive. This method is considered to improve the adhesion force of the rubber bush by performing chlorination treatment. However, as a result of performing a trial manufacture based on the disclosed information, it is confirmed that the rubber surface is roughened by the chlorination treatment and the adhesion force improved to a certain degree by anchor effect, but that the adhesive strength of the vulcanization bonding produced by the adhesive alone is by far insufficient for the rubber breaking to occur. Further, also in this method, the bush and the bracket are merely fixed with a clamp, thus the problem of generating a strange sound in this portion or the problem of abrasion and breaking caused by intrusion of foreign substances cannot be dealt with.